Intel shows why they want Mantle, DX12 support in mobile

18 August 2014

By Wesley "CataclysmZA" Fick

While AMD carries on their work with Mantle, Microsoft’s engineers are toiling behind the scenes to complete work on DirectX 12, the company’s first attempt at a low-level API for the desktop market. DirectX 12 may be the biggest shift for Microsoft since DirectX 10 forced everyone to install Vista and they’re being very careful of how they handle this launch to ensure that more customers don’t shy away to other platforms.

In the past Intel has approached AMD about the Mantle specification in order to optimise their chips for it because it brings a big boost to battery life and performance in thermally constrained environments. Today, we get to look at some of the benefits that Intel is hoping to bring to the Windows platform with DirectX 12-compatible hardware.

At Siggraph 2014 Intel’s Andrew Lauritzen showed a demo that looked a lot like Star Swarm running on a Microsoft Surface Pro 3. Just like Star Swarm’s ships battle, Intel’s demo renders close on 50,000 individual asteroids which Lauritzen claims are “fully dynamic and unique.” The demo is able to switch between a DirectX 11 and DirectX 12 rendering path at the click of a button, giving Intel the ability to see performance changes on the fly without rebooting the demo.

In DirectX 11 mode the demo mostly runs with a 19fps average on the Surface Pro 3, which packs in a Core i7-4650U with Intel HD5000 graphics. It’s not Iris Pro levels of performance, but it’s decent nontheless. What’s evident in the demo here looking at overall system power usage is that DirectX 11 is loading the CPU and GPU equally with work, more or less forcing the processor into its highest boost state to make up for the graphics weaknesses.

This means that the maximum TDP level that the processor is rated for is pretty much maxed out. Performance is middling and it would mean that most users would drop to lower settings to maintain a playable framerate, putting a larger load on the CPU.

Switching to DirectX 12 in Lauritzen’s tests changes things just as dramatically as AMD’s Mantle API changed things for their lower power-weaker CPU. Now the average framerate jumps to 33fps with the same amount of asteroids on-screen and CPU and GPU power is less balanced. The power graph’s timeline shows the exact moment when the jump was made to DX12 and CPU power is now much more constrained to allow for the HD5000 GPU to clock up to its maximum boost rate.

This would have a noticeable effect on heat and battery life, as the more power-hungry CPU cores are being spooled down to make space for the GPU, which is more efficient for the task at hand.

I’ve heard the question of why Intel would want Mantle or DirectX 12 for their products when they’re already superior and the answer is that they don’t have anything like AMD’s Resonant Clock Mesh (RCM) technology present inside their Richland and Kaveri APUs. RCM balances out the power draw to the CPU and GPU within the TDP level according to the workload, allocating more thermal headroom to the GPU when the load requires it.

AMD had to develop RCM as a way around the thermal constraints of their APUs because Global Foundries isn’t offering a 20-nanometer process just yet and the only way they could otherwise improve performance is to underclock their APUs more. In Kaveri, the GCN cores offer more performance at the same clock speed as their outgoing VLIW4-based GPUs inside Trinity and Richland, which is why AMD didn’t go bonkers-mad with their specifications.

Intel’s Haswell processors can technically do this as well but it’s a more manual process, whereas AMD’s solution is a hardware-based one that works no matter what software you’re running.

It will be interesting to see how Microsoft’s new API changes things for Intel and AMD on the integrated graphics front. Readers of my Laptop Buyer’s Guide will remember that I focused on particular hardware configurations geared towards some moderate gaming performance, picking Intel’s HD4400 and AMD’s Radeon HD8520 as the baseline for somewhat acceptable gaming performance on these light, mobile machines.

Mantle, should Intel support it, along with DirectX 12 will give those notebooks the same performance boost as well, making them a lot more useable for applications that demand more GPU horsepower.

Roll on Windows 9, I guess. This will be an interesting launch to keep track of.

Something like that, yeah. Intel’s HD4400 and HD4600 GPUs are perfectly serviceable for low-end gaming. Something like 720p or 768p is doable and it’s currently not that much slower than AMD’s iGPUs. With Mantle, Intel would be able to optimise power delivery so that the iGPUs perform better just like in this benchmark. So one day people would be able to buy the equivalent of the Core i3-4330 with two HT cores and a HD4600 GPU and game just as well as the A10-6600K or A10-7600K.

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